The present invention relates to a solar power generation apparatus and a control method therefor and, more particularly, to a solar power generation apparatus with a solar battery array comprised of a solar battery string formed by a plurality of series-connected solar panels.
In recent years, as the power demand increases, solar power generation systems spread, which serve to compliment a large-scale power plant and can be interconnected to a commercial power system. Currently, to operate a system interconnection solar power generation system, its safety must always be strictly ensured. When the power generation system is not to be interconnected to the commercial power system but is to be used independently, it is also preferable that its safety be always strictly ensured. In order to make the solar power generation system more popular for homes in the future, power must be supplied to the user stably in a particularly safe state without letting the user aware of it, and a system having such a function is required.
FIG. 7 is a view showing an example of a solar power generation system. This system is comprised of a solar battery array 101 as a DC power supply, a collector box 102 for collecting an output from the solar battery array 101, a power conditioner 103 serving as a power converter, and a load 104. The power conditioner 103 has an inverter 106 with un-isolated input/output terminals, and an interconnection protecting relay 107.
The solar battery array 101 may be appropriately formed so that it can obtain an output voltage necessary as a solar power generation system. In a private home-use 3-kw output solar power generation system interconnected to single-phase 200 V, considering the conversion efficiency of the power conditioner 103 and the maximum open-circuit voltage, the solar battery array 101 is preferably formed such that the input voltage (operation voltage) of the power conditioner 103 becomes approximately 200 V. In the arrangement shown in FIG. 7, when an abnormality occurs in the solar battery array 101 or on the electrical path from the solar battery array 101 to the power conditioner 103, the operation of the inverter 106 is stopped and the interconnection protecting relay 107 is opened.
Japanese Patent Publication No. 61-18423 discloses an arrangement in which when a power conditioner 103 is stopped, an output from an solar battery array 101 is short-circuited, as shown in FIG. 8. With the arrangement of FIG. 8, when a ground fault abnormality of the solar battery array 101 is detected, a ground fault switch 111 is closed, so that the output voltage from the solar battery array 101 can be set to 0 V. In the arrangement shown in FIG. 7, even if an abnormality such as a ground fault occurs and the operation of the power conditioner 103 is stopped, the solar battery array 101 keeps generating, as the output voltage, an open-circuit voltage corresponding to the number of solar battery strings (the number of series-connected solar panels) until a person in charge of repair fixes the abnormality.
It is also possible to form a solar power generation system by setting in advance the output voltage from the solar battery strings to a low voltage, in other words, by suppressing the number of strings. In this case, if the system is to be interconnected to a 200-V system, the step-up ratio of the power conditioner 103 increases, and accordingly the conversion efficiency degrades.
In the arrangement of FIG. 7, even when an abnormality occurs in one string, the operation of the entire solar power generation system must be stopped. This applies to the arrangement of FIG. 8, that is, the entire system must be stopped when an abnormality occurs.
When a cable connecting the solar battery array 101 and collector box 102 is damaged to cause a ground fault, the short-circuit current continues to flow to the damaged cable portion to overheat it.
The present invention has been made to solve the above problems separately or altogether, and has as its object to ensure the safety of a solar power generation system without degrading a conversion efficiency.
In order to achieve this object, according to the present invention, there is provided a solar power generation apparatus that comprises a solar battery string which is formed by a plurality of series-connected solar panels, a detector for outputting an abnormality detection signal upon detection of a ground fault in the solar battery string, and at least one switch which is provided midway along the solar battery string and shifted to an open state by the abnormality detection signal.
It is another object of the present invention to eliminate the necessity for stopping the operation of the entire solar power generation system when short circuiting occurs in part of a solar battery array.
In order to achieve this object, according to the present invention, there is provided a solar power generation apparatus comprising a plurality of solar battery strings each of which is formed by a plurality of series-connected solar panels, wherein the plurality of solar battery strings are parallel connected a plurality of detectors for detecting a ground fault in units of the plurality of solar battery strings, wherein the detectors output an abnormality detection signal upon detection of a ground fault, and a first switch for each solar battery string which is provided midway along each solar battery string, wherein the first switch corresponding to one of the solar battery strings is shifted to an open state by the abnormality detection signal associated with the one of the solar battery strings. A second switch is provided for each of the solar battery strings to disconnect the solar battery string from remaining ones of the solar battery strings, wherein the second switch is shifted to an open state by the abnormality detection signal generated by a corresponding one of the detectors.
It is still another object of the present invention to prevent, when a cable connecting a solar battery array and a collector box is severely damaged, the damaged portion from overheating.
In order to achieve this object, according to the present invention, there is provided a control method of a solar power generation apparatus having a solar battery string formed by a plurality of series-connected solar panels, and at least one switch provided midway along the solar battery string and shifted to an open state by an abnormality detection signal, comprising the step of shifting the at least one switch corresponding to the solar battery string where a ground fault has occurred to an open state when a ground fault in the solar battery string is detected.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.